1. Field of the Invention
The present invention relates to an optical recording card.
Recently, cards with various information recorded therein, such as ID cards, cash cards and bank cards have been widely used. The term "optical recording card" is often used as synonymous with optical memory card.
2. Description of the Related Art
Cards of this type are recorded with various information such as personal data, company data and so on. Such information has been recorded at an earlier stage in the form of visible characters or symbols and at a later stage in the form of electric signals using magnetization. However, there is a need of preventing falsification and of increasing the amount of information.
To this end, a laser card has recently been developed using the semiconductor laser technology. A laser card is provided with information recording medium (optical recording medium) having an optical reflective surface on which concavity and convexity serving as data pits are formed. Data pits are detected to read the information, using a semiconductor laser in accordance with a difference in reflection factors of the concavity and convexity.
As particularly shown in FIG. 12 and FIG. 13, an optical recording card 101 has a data truck 102 thereon. The data truck 102 has a plurality of pit columns 104d, 104e, 104f, 104g, . . . composed of a number of pits 103 aligned on a straight line in the column direction. The data truck is read one pit column after another with an optical reading element 106 by displacing the card 101. A number of optical reading elements 106 aligned on a straight line constitutes a line sensor 105. The line sensor 105 disposed over one pit column is sequentially scanned to read one pit column by one scan.
However, with a conventional optical recording card reader for reading information written in the card with a line sensor 105, it is not possible to correctly read the information unless the pit column 104 on the truck and the line sensor 105 are aligned correctly. FIGS. 13 and 14 show examples of arrangements of the pit column 104 and the line sensor 105 reading the pit column.
Assuming the lateral width of the pit 103 is b and the length of the pit column 104 is c, if the inclination of the line sensor relative to the pit column becomes greater than an angle .theta., the line sensor 105 becomes displaced from one pit column to another. Thus, the line sensor 105 will read the gap between pit columns or the other pit column. Even if the inclination is smaller than .theta., the line sensor 105 may become displaced from a pit column to be read and may read the gap or the other pit column on condition a read start position d is near the other pit column.
In view of the above, it is necessary to feed the card precisely in order to read it. However, a precise feeding mechanism for adjusting the inclination of a card so as to align a line sensor and a pit column on the card correctly is not practically possible for an optical recording card of a high density data pit. Even if such a precise feeding mechanism is developed, the system with such a mechanism installed on a card reader will become not only bulky but also very expensive. Alternatively, if an inclined data pit column is intended to be corrected and restored using software, the burden on the software becomes substantially great.
In consideration of the above circumstances, it has been desired to develop a technology by which a reading precision can be attained even if the pit column on the truck of an optical recording card and a line sensor are disposed inclined relative to each other.
An example of conventional technology for a skew correction system for an elongated optical data recording medium is described in the specification of U.S. Pat. Application Ser. No. 617,630, now U.S. Pat. No. 4,588,882, which shows some unsatisfactory results.